Engines of all types require a smooth supply of fuel to ensure reliable operation. When the flow of fuel is interrupted, cut off, reduced, contaminated or impaired in other ways, the leanness of mix, combustion efficiency, temperature, degree of pollutive byproducts as well as basic engine output and other performance aspects can all be affected.
The problem of a compromised fuel supply is an issue under a variety of conditions. One such condition occurs when the engine develops a high temperature in its components. This can occur for example in marine engine systems, particularly fuel-injected systems, when an engine is run for a while and reaches operating temperature, and then is shut off. In this situation, the components in the engine box, including fuel delivery parts such as pumps, hoses, fuel injector rails and fuel injectors reach a high operating temperature. This can be worsened when the engine and other components are exposed to a hot sun.
When fuel that is located inside of a fuel line, engine part or other crucial component reaches a high enough temperature for enough time under those conditions, the fuel can vaporize. This can happen in a parked boat, but can also occur in automotive and other vehicle engines, as well as in industrial engine applications. The interruption of fuel flow due to the process of developing pockets of vapor is known as "vapor lock".
The trapped volume of vapor impedes the flow of fuel by infiltrating the fuel pump, which delivers fuel to fuel injectors. After the vapor volume enters the fuel pump, the pump may not be able re-establish a prime on the fuel. Vapor pockets can also congregate around fuel filters, water separators and other components. When vapor lock occurs, it is usually difficult or impossible to restart the engine at the time of the failure. The engine and other components must be permitted to cool down to condense the vapor pocket, the pocket must be bled off, the pump must be re-primed, and/or other measures must be taken to supply the engine with fuel again. This is a problem for boats on the water, as well as other situations.
Engine systems are susceptible to a number of other fuel supply difficulties. One is air ingestion. When a vehicle rocks or turns violently, as may happen in a banking boat and other situations, the fuel in the fuel tank or tanks can slosh and shift, causing air bubbles to form and enter the fuel line. Air can also enter an engine system when the fuel in a fuel tank runs low, and the pickup tube begins to draw air. However formed, when an air pocket enters a fuel injector or other engine part, the engine can stall and be damaged. Even when an air pocket is passed through the system without direct damage, the components can overheat because liquid fuel normally acts as a coolant.
Engines of different types are also vulnerable to fuel which is contaminated by rust, grit, dust or other particles, which cause abrasion to the .engine and other parts. Engines are also susceptible to problems from water entering the fuel line. Fuel pumps and electronic fuel injectors can tolerate only a small percentage of water contamination, and will eventually fail from water exposure. Water, being denser than fuel, can also fall into the bottom of tanks, pumps and other parts and block the passage of fuel entirely. Water can get into the fuel supply by condensation inside the fuel tank, particularly under humid conditions, may be present in fuel when the tank is supplied, or can originate in other ways.
Engines, marine and other, are therefore subject to a variety of fuel supply problems that can degrade performance. Attempts have been made to insulate the engine from those types of problems. U.S. Pat. No. 5,368,001 to Roche for instance discloses a marine fuel system with a cylindrical body (26) fed by a low-pressure pump. The body contains a small pump (24), which gathers the fuel, under valve and float control, and delivers it under pressure to a fuel injector. Fuel vapors caught in the top (36) of the body are routed back to the engine for burning, or bled off into an absorbing filter.
While a system like that illustrated in U.S. Pat. No. 5,368,001 can help to regulate and to some extent filter the flow of fuel to an engine, certain difficulties with a fuel system of that type remain. For one, that system admits fuel into the reservoir only under control of an inlet valve (50) combined with a float (62), and other mechanical components. The presence of those components subtract from the flexibility and reliability of that system. Any valve, float or other mechanical component can become stuck, when clogged with debris or otherwise. Moreover, such components are typically made of some type of metal, which wears and oxidizes over time and eventually requires removal, cleaning or replacement. Sharp physical impact can also cause mechanical parts to malfunction.
In addition, in a fuel system like that of U.S. Pat. No. 5,368,001 excess vapor does not always vent to atmosphere, instead reaching the engine or an absorbing filter so that vapor pressure is not directly dispersed. Also, the system is not free-running, and relies upon mechanical valving to meter flow on and off during certain circumstances. When the inlet valve (50) of that system is closed, the pump may not reprime until the pressure is relieved. Moreover, in the event of a pump failure in a fuel system like that of U.S. Pat. No. 5,368,001, the excess pressure would be expelled through the vapor vent circuit and ingested into the engine. The resulting surge of extra fuel into the intake manifold would flood, and possibly stall, the engine. Other systems attempt to address different problems of engine fuel supply performance, but not in a complete or satisfactory way.